Sunnyside is a former city in Carbon County, Utah, United States.

Before its merger with East Carbon, Sunnyside had a total area of 3.1 square miles (8.1 km2), all of it land.

30.0% of all households were made up of individuals (single person) and 16.9% had someone living alone who was 65 years of age or older.

In 1883, the Denver and Rio Grande Western Railroad (D&RGW) extended its line from the railhead at Deseret to Price.

By 1901, the D&RGW and its subsidiary, Utah Fuel Coal Company, acquired the operation.

For fifty years, Utah Fuel operated the coal mines in Sunnyside, selling its interest to Kaiser Steel Corporation in 1949.

The financial investments of these companies turned Tidwell's mining operation into a major coal industry, inextricably tied to Sunnyside.

Instead, the office was held by the Superintendent of Mines for Utah Fuel, then later by Kaiser Steel Corporation when it took over in 1950.